In many cases of spinal injury, cerebral hemorrhage and softening of the brain, after an operation the patient develops symptoms such as dysuria or urinary incontinence. In such cases, urethral catheterization using a catheter is adopted in order to secure a smooth urinary passage. This is done in order to maintain kidney functions or prevent or promote the leakage of urine. The catheters used in such cases are called urethral catheters. Such catheters must have sufficient flexibility, elasticity and innoxious property because of their use. Almost all of them are composed of a material such as an olefin polymer, diene polymer or silicone polymer as the base material.
Since catheterization is a remarkably useful curative means for carrying out rapid urination, it is frequently used in fields other than urology such as surgery, internal medicine and obstetrics and gynecology. However, the procedure is defective in that the occurrence of infection is nearly unavoidable if the urethral catheter is inserted into the urinary tract. Since the urethral catheter is left in the urinary tract for a long time, microbes intrude into the urinary tract through the catheter frequently causing symptoms such as urethritis, cystitis or pyelitis. It has been reported that performing an opening continuation catheterization which is frequently used hitherto (a method of collecting urine in a container such as a glass bottle which is not sterilized), infection occurs within 3 days in 42 to 80% of the clinical test and the infection is observed in all cases after the 7th day.
Therefore, with respect to prevention of urinary tract infection, methods such as washing of the bladder or injection of antiseptics or disinfectants are utilized. However, such procedures are disadvantageous because the operation is troublesome and the operation itself becomes a new source of infection.
Further, chemotherapy such as preventive administration of antibiotics, etc. has been carried out. However, it is said that chemotherapy is sometimes even rather harmful due to problems in the administration of large amounts or, even a small amount of antibiotics depending upon the kind of antibiotics. The administration frequently causes an ill effect and a microbe-exchange phenomenon may easily appear if an infection is caused. Thus, topical utilization is generally more desirable for antibiotics.
With respect to topical utilization of antibiotics, a method has been proposed which comprises applying an ointment containing antibiotics to a urethral catheter and a method which comprises coating the wall of the catheter with a resin to form a coating layer in which antibiotics are contained (Japanese Patent Publication No. 27680/79). However, in these cases, the catheter cannot be satisfactorily used, because the antibiotics flow outside the body within a very short time by urine after insertion of the catheter, whereby the antimicrobial function cannot be observed within a short time, because the antibiotics are merely adsorbed on the supporting layer.
Another method involves directly dropping a diluted solution of antibiotics into the bladder using a so-called three-way catheter. This method is only utilized in some areas of urology and it cannot be used in other clinical fields under existing circumstances, because handling is difficult and troublesome.
Intrusion passages of microbes include: (1) counter-current intrusion through a space between the urethral catheter and a mucous membrane of the urinary tract (outside tract passage), (2) intrusion through a bonding part of the urethral catheter and a conduit (including treatments such as washing, etc.), and (3) counter-current intrusion in the interior of the conduit and the urethral catheter from a urine collecting part (inside tract passage). In case of intrusion by the outside tract passage, microbes which are usually present in the urethra rapidly intrude upwards along the wall of the urethral catheter in the early stage of insertion of the catheter and reach the neck part of the bladder. For such infection, the antibiotics which are present on the wall of the urethral catheter exhibit their antimicrobial function, because they can directly touch the microbes. However, microbes intruding through the inside tract passage, for example, microbes intruding from a urine collecting means, namely, microbes dropping or intruding in the urine collecting means, multiply in the urine collected and reach the bladder with back flow urine or rising bubbles. In fact, in an experiment under a static state, it has been ascertained that microbes go backwards in urine in a manner similar to carp ascending a waterfall. Since antibiotics are present on the wall of the urethral catheter, they cannot directly touch microbes intruding from such a passage, and there is the possibility that microbes which are not affected by the antimicrobial function will remain. Therefore, sufficient ability to prevent infection has not been obtained. In order to prevent infection from all intrusion passages, it is necessary for the antibiotics to be present on the wall of urethral catheter and also be gradually released from the wall of the catheter to diffuse into urine so that they contact microbes ascending and wafting in the urine. Therefore, the rate of which microbes separate from the wall is important. As described above, when a method which comprises applying antibiotics or an ointment containing antibiotics to the catheter or a method which comprises coating the wall of the catheter with a resin containing antibiotics is used, the antibiotics easily flow outside the body with the flow of urine. Accordingly, within a short period of time, both the wall and the urine do not contain the antibiotics. Therefore, the ability to prevent infection is completely eliminated within a very short period after insertion. In order to prevent infection, it is important to keep the concentration of antibiotics in the urine at an effective value or more for a long period of time by controlling the rate of antibiotics released from the wall. However, urethral catheter having this ability are as yet unknown.